The invention relates to a coloured electric lamp provided with a glass lamp vessel sealed in a vacuum-tight manner, an electric element in the lamp vessel and a coloured translucent interference filter of alternating layers of high and of low refractive index on the lamp vessel, the layers of low refractive index mainly consisting of SiO.sub.2, which alternating layers have an optical thickness n.times.d which is a fraction of the wavelength .lambda..sub.0 with maximum reflection. Herein, n is the refractive index of a layer and d is its geometrical thickness.
Such a lamp is known from DE GM 86 00 642.
Due to the fact that the materials used in an interference filter mostly have greatly different properties and one material or both materials can also be greatly different from the material of the lamp vessel in this respect, stresses can occur in an interference filter. These stresses can lead to an insufficient adherence of the filter to the substrate and can even cause the filter to scale off, in which event also splitters can chip off the substrate.
In order to counteract an insufficient adherence of the interference filter, the number of layers of such a filter must be limited. However, a small number of layers yields a less selective filter than a large number of layers. This becomes manifest, for example, in the colour saturation of the light transmitted by the filter.